Safety switch device for power operated tools



Oct. 12, 1965 L. E. ELLISON SAFETY SWITCH DEVICE FOR POWER OPERATED TOOLS Filed NOV. 7, 1962 l/ A V Q 4 46 i N s 52 mm 3 5e E/ 2i h s N 2a A FIG. 2

FIG. I

Lynn E. Ellison INVENTOR.

BY gamma M United States Patent 3,211,855 SAFETY SWITCH DEVICE FOR POWER OPERATED TOOLS Lynn E. Ellison, 476 Golf Road, Crystal Lake, Ill. Filed Nov. 7, 1962, Ser. No. 235,996 2 Claims. '(Cl. 20087) This invention relates to safety devices for controlling electrically driven power tools. In particular the invention relates to the use of a magnetically actuated sw1tch in the power circuit of such tools, whereby operation of the tool is prevented unless an adjusting key used in association with the power tool is placed against the face of the switch.

Many power driven machine tools, such as drill presses and lathes, have rotary chucks the jaws of which must be adjusted by means of a wrench or key which is generally fabricated of steel. It sometimes happens that the operator forgets to remove the key from the chuck after the chuck jaws have been set. Operation of the machine with the key remaining in the chuck creates a serious safety hazard since the key is frequently caused to rotate at high speed and thrown free of the chuck with considerable force. The prior art has provided switch means in the power circuits of machine tools whereby operation of the tool is prevented until the adjusting key has been placed in or upon the switch. Such safety devices have not proved to be entirely satisfactory, since they are easy to jam in the closed position by an operator who is unwilling to take the trouble to replace the key in the required position after adjustment of the machine is made.

It is a primary object of this invention to provide a safety switch for use in conjunction with machine tools which will prevent operation of the tool until the adjusting key has been placed against a face plate which forms a part of the switch. Another object of this invention is to provide a safety switch for machine tools which automatically secures an adjusting key in fixed position when the key is placed against a face plate which forms a part of the switch. Yet another object of this invention is to provide a safety switch which provides a readily accessible and convenient means for holding the key.

The invention is best described with reference to the drawings, of which:

FIG. 1 is a perspective view of a drill press equipped with a safety switch in accordance with this invention, and,

FIG. 2 is a side elevational view, partly in section, of switch means which may be employed in accordance with this invention.

Drill press is provided with an adjustable chuck 12 which requires the use of an adjusting key which is separate from the drill press. Drill press 10 is provided with a power input circuit 14, a manually operated on-off switch 16, and a magnetic safety switch 18. Referring to FIG. 2, a safety switch 18 is shown to comprise a housing or switch box 20, and a smooth face plate 22 which is fabricated of a non-magnetic material such as aluminum, polyethylene, Bakelite or other non-magnetic metallic or non-metallic materials. Secured to plate 22 and disposed within box 20 is a magnetically actuated, normally open switch indicated generally by the numeral 24. The switch 24 includes molded switch base 26 which is fabricated of an electrically insulating material. Fixed electrical contact 28 and movable electrical contact 30, which may be made of beryllium-copper, are supported from switch base ice 26. Electrical connection to contacts 28 and 30 is conveniently made by means of screws 32 and 34 respectively. Two magnets, 40 and 42, are supported by means of a ferrous metal support plate 44. Magnets 40 and 42 are arranged with opposite polarity as shown, so that the placing of a ferrous object such as chuck adjusting key 46 in proximity to face plate 22 will form a closed series magnetic circuit comprised of magnets 40 and 42 together with support plate 44 and key 46. By this specific design, maximum attraction between the magnets and key 46 is obtained, whereby magnets 40 and 42 together with supporting plate 44 advance towards the inner surface 48 of face plate 22. The magnets also operate to secure key 46 tightly against the external surface 50 of face plate 22.

Support plate 44 is movably supported from switch base 26 by means of a pair of rebent spring elements 52 and 54. A plunger 56, which is fabricated of an electrically insulating material, is secured to support plate 44 and shaped to actuate movable contact 30 to separate contacts 28 and 30 when magnets 40 and 42 are in a position more remote from the surface plate 22. It will be understood that resilient contact 30 is adopted to make connection with contact 28 when no external force is applied to it. Rebent spring elements 52 and 54 are of higher spring constant than resilient contact 30 and adopted to force contact 30 to the open position When no magnetic material is positioned within the field of magnets 40 and 42. Thus the contacts are normally in the open position. When a magnetic object, such as steel key 46, is placed in proximity to the external surface 50 of face plate 22, magnets 40 and 42 act upon the magnetical object and advance towards the inner surface 48 of face plate 22 against the resiliency of springs 52 and 54. The magnets eventually come to rest against surface 48 of the face plate, and contact 30 moves under the influence of its natural resiliency to make connection with contact 28. The magnets also hold the key 46 tightly against the external surface 50 of the surface plate to retain it in fixed position.

While the invention has been described with reference to a preferred embodiment illustrated in the drawing, it will be evident to those skilled in the art that numerous other switch structures may be employed which will serve the dual functions of closing the power circuit to the machine tool when the key is placed adjacent to the switch face plate, and retain the key in this position by magnetic attraction. For example, the magnetic switch may employ a single movably supported magnet, together with a pair of contacts, and means for opening or closing the contacts in response to movement of the magnet. Optionally, the key may provide the magnet and the switch merely include a magnetically attractable mass which is movably supported and attached to actuate normally open contacts to move them to the closed position.

What is claimed is:

1. In combination with an electrically powered tool having an adjustable driven element and a key fabricated of a ferrous metal for adjusting said driven element, the improvement comprising switch means for controlling electric power input to said tool including a box having a face plate fabricated of a non-magnetic material, said face plate providing an exposed surface externally of said box, a support member fabricated of a ferrous metal disposed within said box, first and second magnets supported by said support member with the north pole of said first magnet and the south pole of said second magnet adjacent said supportmembe-r, spring means for supporting said support member and magnets for movement from a position nearer said face plate to a position more remote from said face plate and yieldably forcing said support member and magnets to the position more remote from said face plate, a pair of electrical contacts responsive to movement of said support member whereby said contacts are closed when said support member is in said nearer position, but not otherwise, whereby when said key is placed against said exposed surface of said face plate said magnets and support member advance toward said face plate, said contacts close, and said magnets,support member, and key together form a single closed series magnetic circuit to hold said key securely against said face plate.

2. An apparatus in accordance with claim 1 in which one of said contacts is rigid and the other is movably supported and yieldably urged to the closed position, and including an electrically insulating projection operably supported by said support member and shaped to connect with and move said movable contact to the open 4, position when said magnets move to the position more remote from said face plate.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Tiefenbach, German application 1,113,496, printed September, 1961.

BERNARD A. GILHEANY, Primary Examiner.

20 ROBERT K. SCHAEFER, Examiner. 

1. IN COMBINATION WITH AN ELECTRICALLY POWERED TOOL HAVING AN ADJUSTABLE DRIVEN ELEMENT AND A KEY FABRICATED OF FERROUS METAL FOR ADJUSTING SAID DRIVEN ELEMENT, THE IMPROVEMENT COMPRISING SWITCH MEANS FOR CONTROLLING ELECTRIC POWER INPUT TO SAID TOOL INCLUDING A BOX HAVING A FACE PLATE FABRICATED OF A NON-MAGNETIC MATERIAL, SAID FACE PLATE PROVIDING AN EXPOSED SURFACE EXTERNALLY OF SAID BOX, A SUPPORT MEMBER FABRICATED OF A FERROUS METAL DISPOSED WITHIN SAID BOX, FIRST AND SECOND MAGNETS SUPPORTED BY SAID SUPPORT MEMBER WITH THE NORTH POLE OF SAID FIRST MAGNET AND THE SOUTH POLE OF SAID SECOND MAGNET ADJACENT SAID SUPPORT MEMBER, SPRING MEANS FOR SUPPORTING SAID SUPPORT MEMBER AND MAGNETS FOR MOVEMENT FROM A POSITION NEARER SAID FACE PLATE TO A POSITION MORE REMOTE FROM SAID FACE PLATE AND YIELDABLY FORCING SAID SUPPORT MEMBER AND MAGNETS TO THE POSITION MORE REMOTE FROM SAID FACE PLATE, A PAIR OF ELECTRICAL CONTACTS RESPONSIVE TO MOVEMENT OF SAID SUPPOORT MEMBER WHEREBY SAID CONTACTS ARE CLOSED WHEN SAID SUPPORT MEMBER IS IN SAID NEARER POSITION, BUT NOT OTHERWISE, WHEREBY WHEN SAID KEY IS PLACED AGAINST SAID EXPOSED SURFACE OF SAID FACE PLATE SAID MAGNETS AND SUPPORT MEMBER ADVANCE TOWARD SAID FACE PLATE, SAID CONTACTS CLOSE, AND SAID MAGNETS, SUPPORT MEMBER, AND KEY TOGETHER FORM A SINGLE CLOSED SERIES MAGNETIC CIRCUIT TO HOLD SAID KEY SECURELY AGAINST SAID FACE PLATE. 